In lithography techniques, steps are performed in which, for example, a resist film comprising a resist composition is formed on a substrate, then selective exposure is performed on the resist film through a mask with a predetermined pattern by radiation such as light and electron beams, and developing is performed so as to form a resist pattern having a predetermined shape on the resist film.
Resist materials, in which the exposed portions are converted to be soluble in a developing solution, are referred to as the positive type, and resist materials, in which the exposed portions are converted to be insoluble in a developing solution, are referred to as the negative type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of miniaturization of patterns.
Typically, these miniaturization techniques involve shortening of the wavelength of the exposure light source. Conventionally, ultraviolet radiation such as g-lines or i-lines have been used, but currently, the mass production of semiconductor elements using KrF excimer lasers or ArF excimer lasers are starting.
Moreover, F2 excimer lasers, electron beams, EUV (extreme ultraviolet), and X rays, whose wavelengths are shorter than those of the aforementioned excimer lasers, are also being examined.
Resist materials are required to have lithography properties such as sensitivity to the aforementioned light source and resolution which is high enough to reproduce patterns with very fine dimensions
As resist materials which fulfill the aforementioned requirements, a chemically amplified resist is used, which includes a base resin that displays changed alkali solubility under action of acid and an acid generator that generates acid by exposure. For example, a chemically amplified positive resist includes a resin, in which the alkali solubility increases by the action of an acid, as a base resin; and an acid generator, and when an acid is generated from the acid generator by exposure in the formation of a resist pattern, the exposed portions are converted to an alkali soluble state.
Until recently, polyhydroxystyrene (PHS) or the resins (PHS-based resins) in which the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups, which exhibit a high degree of transparency relative to a KrF excimer laser (248 nm), have been used as the base resin of chemically amplified resists. However, because PHS-based resins contain aromatic rings such as benzene rings, their transparency relative to light with a wavelength shorter than 248 nm, such as light of 193 nm, is inadequate. Accordingly, chemically amplified resists that use a PHS-based resin as the base resin component suffer from low levels of resolution in processes that use light of 193 nm.
As a result, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as the base resin for resists that use ArF excimer laser lithography or the like, as they offer excellent transparency in the vicinity of 193 nm (for example, see patent reference 1).
Also, as a solvent of resist compositions, a mixed solvent of propylene glycol monoalkyl ether acetate and ethyl lactate is used.
[Patent Reference 1] Japanese Unexamined Patent Application, First Publication No. 2003-241835